Coal mining is generally performed utilising either an open cut or alternatively an underground mining method. When coal mining is conducted underground, it is essential that there is sufficient ventilation within the mine for workers. This requires the provision of fresh air from outside, in addition to the removal of potentially harmful waste gasses generated within the mine.
Ventilating remote locations within an underground mine can be particularly difficult to achieve. It is necessary to install and maintain a ventilation circuit including an intake and a separate return airway to the innermost location to be ventilated. Ventilation tubing is typically installed as the mine is cut by a continuous miner, after the roadway has been excavated and the roof supported, prior to further advancement of the continuous miner.
As the roadway and the cutting face advance underground, the final portion of the roadway in front of the continuous miner defines an air flow impasse, which creates a stagnant area, having limited air flow and ventilation. This occurs because the air flow circuit is closed in this region of the mine. This makes it difficult to ventilate at or near the cutting face, where the continuous miner, and any workers operating the continuous miner, are located.
The cutting face is generally ventilated using an auxiliary fan which has ventilation tubes connected to it. The ventilation tubes run from the fan (which is positioned in the return airway) and the tubes are suspended from the roof of the mine, and extend all the way to the cutting face. The fan is used to draw air away from the cutting face, which in turn creates a low air pressure at the cutting face. This results in fresh air from the fresh air supply line being drawn toward the face and also displacing airborne dust and gases away from the area.
As the continuous miner cuts the coal, the cutting face progresses forward and the roof of the roadway is supported using bolts or other support techniques. The continuous miner includes a flexible trunk that is connected to the end of the ventilation tube which is located closest to the cutting face. The flexible trunk is approximately 8-10 metres long. Accordingly, after 8-10 metres of mining, the process of hanging another two ventilation tubes is conducted.
This process requires that the continuous miner is turned off and isolated. It is then necessary to bring in a vehicle such as a diesel vehicle with a man basket on the front and two additional vent tubes located in the man basket.
Typically, the process requires that the diesel vehicle drives behind the continuous miner, two workers get into the man basket and are lifted up to the height of the flexible trunk. The workers then pull the rest of the flexible trunk out of the existing vent tubes and proceed to hang the new ventilation tubes that have been supplied by the basket. After this process is completed, the workers reinstall the flexible trunk to the end of the new ventilation tubes to reinstate ventilation to the cutting face.
The process described above suffers from several inherent drawbacks. Firstly, the removal of the flexible trunk from the last vent tube results in loss of ventilation to the cutting face. This problem is compounded by the fact that the diesel vehicle is typically emitting CO2 gases into the restricted ventilation cutting face area. If the emissions of CO2 or CO or other dangerous gasses reach an elevated predetermined level, this will cause the gas sensors on the continuous miner to trip the power therefore not allowing the miner to continue mining until a statutory official has inspected the area, degased the area and notified the undermanager on shift. Power is then re-established to the continuous miner once gas levels are back within safe mining levels.
Existing ventilation tubes are typically stored within the mine prior to and after use, typically in a cut-through formation, where they are stacked side by side and on top of each other. The large volume of space required prevents the cut-through (or other storage location within the mine) from being utilised for storing other mining equipment.
The existing ventilation tubes are heavy, which creates various manual handling risks when the tubes are being installed, decommissioned or otherwise moved.
A further problem with the existing ventilation system described above concerns downtime in production on account of the time required to install the ventilation tubes which can take from 25-35 minutes to complete and on average needs to be done three times per shift.
A further disadvantage with existing underground ventilation systems concerns the retrieval of the vent tubes. This process typically requires six men and two Jug-A-O machines to reclaim vent tubes for a single panel advance (the block of coal being mined). This process on average usually takes half a shift, and may be necessary once a month. Three men are occupied by the Jug-A-O with the man basket being used to remove the tubes from the roof and drop them down to the floor where another worker loads the tubes that have been dropped onto a second Jug-A-O that is used to take the tubes to a storage area. The operator of the Jug-A-O that is taking the tubes to the storage area is then met by another worker that is waiting to stack the tubes for storage. Disadvantageously, this process is labour intensive, and requires significant amounts of manual handling and lifting of heavy vent tubes.
Typically each vent tube must be manually handled six times from hanging on the roof to the placement in the storage area. Given that approximately 100 vent tubes typically need to be moved for a single panel advance, the amount of man handling is significant.